1. Field of the Invention
The present invention relates to an information playback system, and more particularly to an information playback system for playing back information recorded on a recording disk such as a video disk.
2. Description of Background Information
Information recording disks such as video disks are designed such that, in addition to the audio and video information recorded thereon, address information corresponding to the information in each recording track is also recorded. By utilizing this address information, the so-called random access operation, i.e. playback of a desired part of the recording disk, is enabled.
On the other hand, playback systems for playing back information recorded on a recording disk are generally provided with a pickup positioning system by which a position of the pickup relative to the disk in the radial direction of the disk (i.e. a direction normal to the direction of recording tracks) is adjusted. This pickup positioning system generally comprises a tracking servo device, and a slider translating device such as a slider motor by which a slider member carrying a pickup is translated in the radial direction of the recording disk. By the operation of the tracking servo device, for example including a biasing means such as a tracking mirror, the position of the pickup is shifted in the radial direction of the recording disk so that the information reading point of the pickup such as a laser light spot always traces one of the recording tracks accurately.
The address search operation of the playback system is performed as follows. When a desired address is designated, address information read by the pickup and the designated address is compared. Then, the slider translating device is driven until the difference between the designated address and address information read by the pickup is smaller than a predetermined value, so that the information reading point of the pickup is moved at a predetermined speed. On the other hand, in the case of scan mode operation in which the information reading point of the pickup is moved by a fast forward or reverse operation toward a position in which a desired information is recorded, a control operation is performed so that the slider translating device is moved in response to a manual operation of an operator (user) so that the information reading point of the pickup is moved at the predetermined speed.
In the information playback systems operated in this way, however, the address search operation or the fast forward or reverse operation may not be properly performed for the playback of information recorded on a constant linear velocity type record disk which is to be driven so that the linear velocity of the movement of the recording track is constant (referred to as a CLV disk hereinafter), or a constant angular acceleration type record disk which is to be rotated so that the rate of the variation of the angular velocity is constant (referred to as a CAA disk hereinafter).
More specifically, the rate of rotation of the disk varies depending on the information reading point of the pickup in the case of the CLV disks or the CAA disks. Therefore, if the drive speed of the slider motor is to be controlled constant, the slider translation device should be controlled so that the drive operation of the spindle motor for rotating the record disk follows the translation of the information reading point even between positions through which the rate of rotation of the record disk varies greatly, in order that the address information is read accurately.
Therefore, in the case of the information playback systems of conventional type, it is not possible to raise the speed of the movement of the information reading point during the address search operation. This leads to a relatively long access time of the information playback system. Further, there is a problem that the speed of the playback of recorded information during the fast forward or the fast reverse operation differs largely between the innermost part and the outermost part of the recording tracks of the record disk.